When Brayton Simple Cycle gas turbines operate as mechanical power drive sources to electric generators and other mechanically driven devices, atmospheric air is compressed and mixed with hydrocarbon gases or atomized hydrocarbon liquids for the resulting mixture""s ignition and combustion at constant pressure. To produce power, the hot combustion and working motive fluid gases are expanded to near atmospheric pressure across one or more power extraction turbine wheels, positioned in series.
The majority of Brayton simple open-cycle aeroderivative-style Low-NO.sub.x art gas turbines are predominantly presently limited in achieving shaft output horsepower rating with 34 to 36% thermal efficiencies, whereas most simple cycle industrial-style Low-NO.sub.x art gas turbines are predominantly presently limited in achieving shaft output horsepower rating with 37 to 40% thermal efficiencies. These higher efficiencies are achieved when the gas turbines operate with compressor ratios ranging from 18 to 26 and predominant power turbine inlet temperatures ranging from 180xc2x0 to 2300xc2x0 F.
Existing gas turbines employ combustion chamber air/fuel combustion chemical reactions, wherein the elements of time and high peak flame temperatures increase the presence of disassociation chemical reactions that produce the fugitive emissions of carbon monoxide (CO) and other chemical reactions that produce nitrogen oxides (NO.sub.x).
The best available applied turbine low-nitrogen oxide combustion technology for limiting gas turbine NO.sub.x emissions, using stiochiometric air/fuel primary combustion reaction chemistry means, still results in the production of over one million pounds a year of fugitive emissions, when a 100 megawatt gas turbine facility operates continuously. Such emissions of NO.sub.x and CO are no longer acceptable for new power facilities being built in numerous states and metropolitan environmental compliance jurisdictions, particularly for the more economically popular sizes of 400 MW to 1200 MW power generation plants.
With the conventional gas turbine""s use of compressed atmospheric air as a source of oxygen (O.sub.2), which acts as a fuel combustion oxidizer reactant, nitrogen (N.sub.2) is the 78.1% predominant mass component within the cycle""s working motive fluid. Due to its diatomic molecular structure, the nitrogen molecules are capable of absorbing combustion heat only through convective heat transfer means resulting from their collisions with higher temperature gas molecules or higher temperature interior walls of the combustion chamber.
Despite the very brief time it takes a conventional cycle to reach a molecular primary flame combustion zone gas equilibrium temperature of less than 2600xc2x0 F. to 2900xc2x0 F. within the combustion chamber, there are sufficiently excessive high flame temperatures and ample time for a portion of the highly predominate nitrogen gas to enter into chemical reactions that produce nitrogen oxides. The same combined elements of time and sufficiently excessive high flame temperature permit carbon dioxide to enter into dissociation chemical reactions that produce carbon monoxide gas.
To achieve a goal of greatly reducing a turbine cycle""s fugitive emissions without sacrificing simple and cogeneration power thermal efficiencies, it is necessary to alter both the fuel combustion chemical reaction formula and the means by which acceptable combustion flame temperatures can be precisely maintained within the turbine combustor. Maintenance of an acceptably low fuel combustor gas temperature requires a change in the means by which the heat of combustion can be better controlled and more rapidly distributed uniformly throughout the gases contained within the fuel combustor.
It has been well known and practiced for decades that higher humidity air and injected water or steam in the presence of conventional air working motive fluid increases combustion flame speeds and fuel combustion thermal efficiencies within gas turbines and other apparatus using air/fuel combustion. It has also been well known and practiced that partially re-circulating, combustion flue gases containing carbon dioxide back into a combustion chamber results in a reduced level of nitrogen oxides within the fuel combustion exhaust gases. Due to the high temperatures and speed of completed fuel combustion, the scientific community has been unable to reach a consensus as to precisely what series of altered chemical reactions occur when water vapor and/or carbon dioxide is introduced into a turbine combustion chamber.
Conventional gas turbines must be de-rated from their standard ISO horsepower or kW ratings at ambient temperatures exceeding 59xc2x0 F., or at operating site altitudes above sea level. Thus, during summer""s peak power demand periods, when the temperature rises to 95xc2x0 F., a 19 to 22% horsepower deration of a conventional gas turbine""s ISO rating occurs. It is desirable that a gas turbine cycle not be susceptible to such temperature deration.
Present gas turbines"" high combustor operating pressures require a gas-pipeline source of 280 to over 550-psi gage pressure. If a manufacturing facility, process facility, or utility power generating facility has access only to a lower pressure source of natural a gas, then one or more high horsepower fuel gas booster compressors must be employed to raise the fuel supply pressure. It is therefore desirable that gas turbines be able to operate on fuel gas supply pressures of less than 100 psi gage.
To achieve ultra-low fugitive turbine exhaust emissions, the AES power cycle of the present invention employs a continuous controllable mass flow rate of recycled superheated vapor-state mixture of carbon dioxide (CO.sub.2) and water vapor (H.sub.2 O), in identical mixture Mol percent proportions as each occurs as products of chemical combustion reactions from the gaseous or liquid hydrocarbon fuel employed.
Provided herein is a partially-open gas turbine cycle for use with modified gas turbines, preferably presently designed with a final stage of air compression that has radial means connected to one or more exterior-mounted turbine combustion chambers. The partially-open gas turbine cycle can also be used with alternative power cycle configurations that utilize existing mechanical equipment components which are not specifically designed for, nor applied to, the manufacture of current technology gas turbine systems.
The AES power cycle of the present invention provides a non-air working motive fluid means that reduces mass flow fugitive emissions by over 98% from that of conventional Low-NO.sub.2 designed gas turbines.
The AES power cycle of the present invention offers means of controlling a combustor""s internal temperatures to avoid the creation of fugitive turbine exhaust emissions.
The AES power cycle of the present invention offers the equivalent or higher thermal efficiencies than open simple-cycle gas turbines operating alone or within cogeneration. power facilities. The AES simple-cycle is susceptible to 42.5% output shaft thermal efficiency and, which applied to a cogeneration system, the overall thermal efficiency may approach 100%.
The AES power cycle described herein has turbine compression ratios of 3.0 to 6.5 (3.0 to 6.5 bar operating pressure) with presented example cycle efficiencies at 60 psi absolute (3.12 bar).
The AES power cycle of the present invention offers high thermal efficiencies with turbine fuel gas supply pressures of less than 100 psi gage (7.9 bar).
The AES power cycle and power cycle equipment components described herein include the means by which its turbine power cycle and separately associated power plant auxiliaries are monitored and controlled for safe operation, as well as means of controlling working motive flows in response to changes in power demands. The combined turbine/recycle compressor and driven mechanical equipment safe operating and output functions are monitored and controlled by a turbine manufacturer""s PLC based control panel design that meets or exceeds the American Petroleum Institute (API) specifications for industrial gas turbines (API 616) or aeroderivative gas turbines specification (API RP 11PGT) and may be further control-integrated with a power plant distributive control system (DCS). The individual auxiliary system modular component PLC control panel""s operating output data signals are collectively control-integrated into the DCS together with the operating power cycle""s operating data signals comprising but not limited to:
(a) the AES power cycle""s individual valve controlled gas stream""s mass flows with temperatures and pressures for a given operating hydrocarbon fuel composition and shaft horsepower output;
(b) the AES power cycle system turbine exhaust conditioning status and turbine exhaust excess oxygen content for a given operating hydrocarbon fuel composition;
(c) the AES power cycle""s turbine exhaust and primary recycle compressor discharge mass flow rates through their respective downstream waste heat exchangers"" plurality of parallel positioned heat exchanger sections;
(d) the cycle""s power plant auxiliary rotating equipment""s operating mass flow rates with temperatures and pressures combined with the positioning-state of any rotating equipment""s integral capacity control apparatus.
An additional object of the present invention is to provide a turbine power cycle system that operates with a fuel gas supply pressure of less than 100-psi gage pressure.
It is a further object of this invention to provide the means wherein, during a steady-state power operation, the atmospheric vented and open cycle portion of the turbine exhaust mass flow is susceptible to being only 5.00% of the mass flow rate as contained within the closed portion of the turbine power cycle.
The following four embodiments comprise the subject matter of this invention:
The working motive fluid of this invention""s turbine power cycle system comprises a continuous superheated vapor mixture of predominant carbon dioxide (CO.sub.2) and water vapor (H.sub.2 O) in identical Mol percent ratio proportions as the molecular combustion product components are produced from the combustion of the gaseous or liquid fuel utilized.
Within the predominately-closed portion of the cycle, the turbine exhaust gas is recycled from the turbine exhaust gas distribution manifold, the exhaust gas having a small degree of superheat temperature and positive gage pressure supply, to the inlet of the primary recycle compressor. This recycle compression function may be performed by a typical compressor used for air compression within a conventional gas turbine, or it may be a separate means-driven compressor of the axial, centrifugal, or rotating positive displacement type. Either means of compression incorporates means of flow control available within the compressor or by its driver, with flow changes being initiated by a master system control panel containing programmable microprocessors.
The compressor may increase the recycled turbine exhaust""s absolute pressure by a ratio of only 3.0 to 6.5 to achieve a high simple-cycle thermal efficiency, but the cycle is not limited to operations within these said ratios.
As shown in Table 1, between gas turbine combustor pressures of 45 psia and 75 psia, the AES Cycle thermal efficiencies range between 35.16% and 43.24%. Between 75 psia and 90 psia combustor pressures (with the common primary recycle compressor and power turbine efficiencies of 84% and power turbine inlet temperature of 1800xc2x0 F.), the AES cycle efficience begins to decline.
The recycled turbine exhaust gas (hereafter referred to in the cycle fluid flow as xe2x80x9cprimary recycle gasxe2x80x9d) is discharged from the primary recycle compressor at an increased temperature and pressure through a manifold into two parallel branch conduit means, with the first branch conduit connected to a simple-cycle means included air-cooled heat exchanger, or alternatively to a cogeneration plant means included hot-gas-to-steam waste heat recovery exchanger. The second pressurized recycle gas branch conduit is connected to a counter-current flowing gas-to-gas heat exchanger. Within this exchanger, the high temperature recycle gas""s heat may be transferred to a pressurized steam stream or to a predominant facility""s process gas stream.
The primary recycle gas discharge flow from the two parallel-positioned heat exchangers (described above), is maintained at a slightly superheated vapor temperature at the selected operating pressure slightly above that of the selected internal combustor pressure. The primary recycle gas flows are discharged from the two parallel heat exchangers through their respective conduit branches of a common manifold conduit means, with each branch having a gas mass flow sensor means and a flow control damper valve.
The primary recycle gas is further conveyed through a common conduit means to the dual parallel inlet manifold of the primary section of a power turbine exhaust gas waste heat recovery unit (WHRU) exchanger. This power turbine exhaust gas WHRU exchanger is capable, with the particular example of a methane fuel combustion chamber pressure of 60 psi absolute and 1800xc2x0 F. power turbine inlet temperature, of raising the temperature of the primary recycle gas within the turbine exhaust gas WHRU exchanger to a maximum 1350xc2x0 F.; with these operating conditions and assumed compressor and turbine efficiencies of 84%, the desired cycle efficiencies of 42.5% are achieved. Thereafter, the highly superheated and pressurized recycle gas (hereafter referred to as xe2x80x9cworking motive fluidxe2x80x9d) is separately flow-divided for passage into one or more premixer and combustor assemblies.
From the First Embodiment""s primary recycle turbine exhaust gas conduit routing means to the primary section of the power turbine exhaust WHRU, a portion of the total primary recycle low superheat gas is extracted from two separate branch connections on the conduit means. The first branch supplied portion of the extracted primary recycle gas is supplied to one or more premix assemblies. The second branch supplied portion of the extracted primary recycle gas is supplied to the inlet of a smaller secondary recycle compressor for an additional increase in pressure. This supply of further pressurized and after-cooled secondary recycle gas is routed to a venturi-style gas blender mounted near a power facility system""s air separation unit. Within the venturi-style gas blender, the secondary compressed recycle gas stream is homogeneously blended with the highly predominant oxygen stream produced by a power facility system""s air separation unit.
From the Second Embodiment""s described blending of the recycle turbine exhaust gas and oxygen streams, the blended vapor mixture is routed by conduit means to the one or more turbine premixer sub-assemblies at a low temperature that is a few degrees above the dewpoint of the blended mixture. The Mol percents of the combined carbon dioxide and water vapor within the blended mixture acts as chemical reaction suppressant to potential self-ignition within the conduit means, in the event that the conduit""s mixture inadvertently comes into contact with hydrocarbon containing foreign material.
Each combustor assembly may comprise one or more premix sub-assembly means into which the following streams are introduced: fuel; First Embodiment primary recycle gas; First Embodiment working motive fluid; and Second Embodiment combined recycle turbine exhaust gas and predominant oxygen stream, which originates from an adjacent facility containing an air separation modular system employing membrane air separation, cryogenic or pressure swing absorption method designs. These individual flow controlled conduit streams at differential pressures and velocities are collectively admitted through their respective premixer conduit means for homogeneous blending at their points of admittance into the primary combustion zone of each combustor assembly.
To establish primary combustion temperatures that do not exceed 2400xc2x0 F., the first of two separately controlled mass flow streams of the highly superheated working motive fluid is directed from the turbine exhaust gas WHRU exchanger of the First Embodiment to the premixer with internal means providing for the division of the working motive fluid first stream for functions of: the homogeneous blending of the said motive fluid with fuel gas, predominant oxygen stream, and low superheat primary recycle within the immediate premixer interface area within the combustor; and the directed flow of secondary zone working motive fluid into the outermost flow annulus area surrounding the homogeneous mixture admitted into the combustor for ignition. The secondary zone working motive fluid admitted into the combustor thereby provides a closely positioned rapid heat-absorbing mass shrouding means around each primary zone combustion flame zone developed within the combustor immediately downstream from each premixer. This flame shrouding means enables the radiant heat energy emanating from the binary gas molecules within the flame to be rapidly distributed to and absorbed uniformly by the shroud""s contained identical binary gaseous molecules at the speed of light-rate of 186,000 miles per second. The resulting equilibrium temperature within each combustor""s primary and secondary zone, based on the controlled flow rate of the first stream of working motive fluid into the premixer, may be established as being equal to or less than 2400xc2x0 F.
The second of two separately controlled mass flow streams of the highly superheated working motive fluid directed from the turbine exhaust gas WHRU exchanger is a working motive fluid tertiary flow of the First Embodiment. The tertiary flow may be introduced into the annulus area surrounding the inner combustor liner, followed by its flow emanation into the combustion chamber area through openings in the liner. This tertiary mass flow of highly superheated working motive fluid results in the lowering of the temperature of the final combustor exhaust to a maximum exhaust equilibrium temperature of 1800xc2x0 F. to the power turbine assembly. The equilibrium temperature of the combustor exhaust gases is not limited to 1800xc2x0 F., and may be controlled by the introduced tertiary mass flow rate to reach any other higher or lower selected operating temperature.
Within the power turbine assembly, the combustors"" pressurized and highly superheated gases may be expanded to create useful work in the conventional form of both turbine output shaft horsepower and internal horsepower to additionally direct-drive the primary recycle compressor. In a conventional 2-shaft style of gas turbine, this primary recycle compressor is shaft-connected to the high-pressure section of the power turbine assembly and the low pressure section of the power turbine assembly provides the turbine power output power to driven equipment. The expanded exhaust gases exit the power turbine assembly at a small positive gage pressure, and are further conveyed to the inlet plenum chambers of the combined primary, secondary, and the optional auxiliary parallel-positioned sections of the turbine exhaust gas WHRU exchanger. The combined turbine exhaust gases exit the turbine exhaust gas WHRU exchanger""s combined sections and are further collectively conveyed by manifold means to an air-cooled exchanger that further lowers the exhaust temperature to a controlled temperature level that is slightly above the dewpoint of the 0.5 to 1 psi gage pressure turbine exhaust. The turbine exhaust gases are then further routed to the turbine exhaust gas distribution manifold to complete the closed portion of the invention""s partially open power cycle system.
From the Third Embodiment""s predominately-closed portion of the cycle that is operating in a steady-state condition, excess turbine exhaust in its slightly superheated vapor state is vented from the turbine exhaust distribution manifold, thereby creating the open portion of the power cycle system. The mass flow rate in which the turbine exhaust is vented is essentially equivalent to the mass rate at which the water vapor and carbon dioxide products of combustion are formed within the power cycle system""s one or more combustors. The cycle""s vented excess turbine exhaust gas, during a steady-state partially open power cycle operation, is vented to the atmosphere.
With the partially-open gas turbine cycle power system described herein, fuel combustion means are susceptible to a 98% reduction of nitrogen oxides (NO.sub.x) that occur in current art Low-NO.sub.x gas turbines. These same partially-open gas turbine cycle power system""s fuel combustion means also suppress the chemical reaction dissociation formation of the fugitive emission carbon monoxide (CO) from carbon dioxide (CO.sub.2). The means of suppressing fugitive emissions results from the following collective working fluid molecular attributes and combustion events:
(a) The working fluid of this invention""s power cycle system comprises a continuous superheated mixture of predominant carbon dioxide (CO.sub.2) and water vapor (H.sub.2 O) in identical Mol percent ratio proportions as these molecular components are produced from the combustion of a given fuel. For example, in the case of landfill gas, the working gas fluid contains a 1:1 ratio of 2 Mol carbon dioxide to 2 Mols water vapor in identical proportion to the products of stoichiometric oxygen combustion. The chemical reaction equation can be described as follows:
Working Motive Fluid+1 Mol CH.sub.4+1 Mol CO.sub.2+2 Mols O.sub.2=2 Mol CO.sub.2+2 Mol H.sub.2 O+Heat+Working Motive Fluid.
In the example of methane gas fuels, the working fluid composition contains a ratio of 1 Mol CO.sub.2 to 2 Mols H.sub.2 O in identical proportion to the products of 105% stoichiometric oxygen combustion of methane fuel within the chemical reaction equation of:
Working Motive Fluid+1 Mol CH.sub.4+2.1 Mols O.sub.2=1 Mol CO.sub.2+2 Mols H.sub.2 O+0.1 Mol O.sub.2+Heat+Working Motive Fluid.
(b) The invention""s turbine power cycle system""s working fluid provides the replacement mass flow means to the conventional open Brayton simple cycle""s predominant diatomic non-emissive and non-radiant energy absorbing molecular nitrogen (N.sub.2) working fluid. The invention""s replacement working motive fluid contains both predominant water vapor (with a binary lack of molecular symmetry) and a mass ratio of atomic weights of (16/2)=8 and carbon dioxide with a mass ratio of atomic weights of (32/12)=2.66, which denotes their susceptibility to high radiant energy emissivity and absorption. This compares to the nitrogen""s mass ratio 14/14=1 which denotes nitrogen""s minimal, if any, emissive and radiant energy absorbing abilities at any temperature.
(c) The invention""s turbine power cycle system""s working motive fluid provides the means for a turbine combustion chemistry with a 900% increase of binary molecular mass means susceptible to the fuel/oxidation exothermic chemical reactions being highly accelerated at the speed of light (186,000 miles a second). This enables the complete and rapid combustion of gaseous or liquid hydrocarbon fuels through the absorption and emissive radiant heat transfer of the fuels"" combustion product""s superheated binary carbon dioxide and binary water vapor molecules"" heat energy, that is emitted in the infrared spectral range identical to that of the working motive fluid.
(d) The Third Embodiment described combustor premixer assemblies providing means for homogeneous blending, wherein gaseous streams of working motive fluid and an oxygen-rich stream are further homogeneously blended with the gaseous fuel stream. The gaseous fuel stream also comprises binary molecules of high susceptibility to high radiant energy absorption and emissivity, such as methane with a mass ratio of atomic weights of (16/4)=4, ethane. with a mass ratio of atomic weights of (24/4)=6, propane with a mass ratio of atomic weights of (36/8)=4.5, etc.
(e) The subsequent tertiary zone admission of a controlled-flow of susceptible Table 1 identified 1350xc2x0 F. superheated working fluid into the 2400xc2x0 F. combined primary and secondary zones combustion gas stream, results in an almost instantaneous creation of the maximum desired equilibrium temperature of 1800xc2x0 F. This rapid establishment of the preferred equilibrium temperature is due to the 186,000 miles per second rate of radiant heat transfer between the two streams of common molecular constituents with common means of high radiant energy absorption and emissivity. The extremely rapid rate at which the combustion product gases are lowered in temperature means there is no time for the chemical disassociation reactions, which produce carbon monoxide (CO), or other chemical reactions which produce nitrogen dioxide (NO.sub.2), which may be produced in the presence of the highly elevated gas molecular temperatures above 2600 to 2900xc2x0 F.